Seats of vehicles, such as automobiles, buses, and trains, and furniture, such as sofas and legless chairs, use seat covering materials that are embossed to form a pattern of projections and depressions in the surface to improve the aesthetic quality. Embossing provides a seat covering material with a three-dimensional surface and a desirable aesthetic appearance. In addition, formation of projections and depressions may enhance the tactile properties.
Patent Document 1 describes a conventional embossing process of seat covering materials. The method disclosed in this document passes a lamination sheet, which includes an outer material and a cushion layer, between a heated embossing roll and a heat roll. This forms an embossed pattern in the surface of the lamination sheet.
FIG. 12 shows an embossing roll 100 that is used in the embossing process described in Patent Document 1. The embossing roll 100 includes a base surface 101 from which a plurality of embossing portions 102 projects in a regular pattern. When a lamination sheet passes between the embossing roll 100 and the heat roll, the embossing portions 102 press the surface of the lamination sheet for predetermined duration and with predetermined pressure. This forms a plurality of deep, clear depressions 201 in the surface of the lamination sheet 200 as shown in FIG. 13A. A three-dimensional pattern of projections and depressions is thus formed in the entire surface of the lamination sheet 200.
The embossing portions 102 projecting from the conventional embossing roll 100 substantially have the shape of a rectangular solid. The embossing portions 102 therefore form an embossed pattern in which depressions, which are rectangular as viewed in a front view, are regularly formed in the surface of the lamination sheet 200. As shown in FIG. 13B, the cross-sectional shape of the lamination sheet 200 is defined only by flat heat-pressed portions 202, which are pressed by the embossing portions 102, and non-heat-pressed portions 203, which are not pressed by the embossing portions 102.
Thus, even though the surface of the lamination sheet 200 includes a three-dimensional embossed pattern, the section having the embossed pattern has a monotonous appearance. Further improvements are needed with respect to the aesthetic appearance of seat covering materials.